Light valve fluid thickness regulator



Jan. .13, 1970 H. E. TOWLSON LIGHT VALVE FLUID THICKNESS REGULATO RFiled March 28, 1969 2 Sheets-Sheet 1 i 6 R 2 T C E L E N U G INVENTORZHOWARD E. TOWLSON,

HIS ATTORNEY.

Jan. 13, 1970 H.- EQTOWLSON Y 3,489,941 LIHT VALVE FLUID THICKNESSREGULATOR- Filed March,28, I969 2 Sheets-Sheet 2 INVENTOR HOWARD E.TOWLSON,

BY HIS ATTORN United States Patent 3,489,941 LIGHT VALVE FLUID THICKNESSREGULATOR Howard E. Towlson, Baldwinsville, N.Y., assignor to GeneralElectric Company, a corporation of New York Filed Mar. 28, 1969, Ser.No. 811,431 Int. Cl. H01 29/12 U.S. Cl. 31391 12 Claims ABSTRACT OF THEDISCLOSURE A light modulating fluid layer on the surface of a rotatabledisk of a light valve is maintained smooth and of uniform thickness byuse of a stationary, substantially flat, shaped plate spaced at apredetermined distance from, and at an angle with, the disk. Fluid in asump through which the lower portion of the disk rotates rises bycapillary action in the space between the disk and the plate to form ameniscus boundary, leaving a uniform thickness of fluid on the disksurface in the regions where the disk has moved past the boundary.

This invention relates to light valves for optical projection of imagesgenerated electronically on a fluid layer, and more particularly to aregulator for maintaining the fluid layer smooth and at a uniformthickness.

One form of light valve suitable for optical projection ofelectronically generated images onto a remote display surface comprisesan evacuated envelope containing an electron gun in alignment with atransparent disk. The disk is rotated through a reservoir of lightmodulating fluid to deposit a continuously replenished layer of fluid onthe disk surface. An electron beam, generated by the electron gun, isdirected through electrostatic beam deflecting and focusing means and isscanned across a portion of the light modulating fluid layer so as toselectively deform the layer. The fluid deformations thus formedconstitute diffraction gratings which. in conjunction with a Schlierenoptical system, selectively control passage of light from a light sourcethrough the disk and through an output window in the light valveenvelope in order to create visible images at a remote display surfaceon which the light impinges.

Because the modulating information is applied to the deformable fluidmedium entirely in the form of surface deformations, it is particularlyimportant, in order to minimize spurious images and to obtain uniformdark fields, that the surface of the deformable fluid medium beextremely smooth, uniform, and free from extraneous deformations as itis carried into the regionin which deformation-producing charges are tobe deposited on the medium. This region is known as the raster area. Inaddition, effective control of the deformable medium thickness as itenters the raster area is particularly important from the standpoint ofcontrolling light modulation efficiency and deformation decay time.

Various types of smoothing means have been employed in the past in orderto achieve desired smoothness and uniform thickness of the deformablemedium in light valves. Prominent among the earlier smoothing means isthe mechanical smoothing bar, which merely comprises a blade maintainedat a desired level above the surface supporting the deformable medium.Blades of this type, however, require that the disk surface, as well asthe blade edge, be made flat to a high degree of precision, and thatboth the blade and the disk be positioned with extreme accuracy.Moreover, the blade must be positioned very close to the fluid mediumsupporting surface, not only giving rise to the likelihood that a smallparticle might become lodged between the blade and the disk surface3,489,941 Patented Jan. 13, 1970 and scratch the disk surface as thedisk rotates, but also imposing high torque requirements in order toachieve uniform velocity of disk rotation.

To overcome the drawbacks of the mechanical smoothing bar, the so-calledelectronic dam has been employed. This involves impingement of anelectron beam onto the deformable medium immediately prior to entry ofthe medium into the raster area, in order to smooth the medium, asdescribed and claimed in E. F. Schilling Patent 3,164,- 671, issued Ian. 5, 1965, and assigned to the instant assi-gnee. However, anymomentary power loss may allow some of the dammed fluid to flow into theraster area, causing interference in the displayed image. Moreover, whenthe electronic circuitry is turned on, a certain length of time isrequired after the electronic circuitry has begun functioning before thefluid over the entire raster area has become smooth enough to produce auseable image.

The aforementioned drawbacks of the mechanical smoothing bar areovercome by the present invention. Moreover, the quality of imageproduced by a light valve employing the present invention is unaffectedby momentary power loss and, when the electronic circuitry beginsoperating, the image is available for display immediately.

Accordingly, one object of the invention is to provide smoothing meansfor the deformable fluid medium of a light valve which may be fabricatedwithout a high degree of precision and which may be positioned in thelight valve without extremely accurate positioning requirements.

Another object is to provide smoothing means for the deformable fluidmedium of a light valve which exhibit a very low probability that aforeign particle might scratch the surface of the light valve rotatingdisk.

Another object is to provide smoothing means for the deformable fluidmedium of a light valve which do not impose high torque requirements onthe light valve rotating disk.

Another object is to provide smoothing means for the deformable fluidmedium of a light valve which permit production of an image immediatelywhen the electronic circuitry begins operating and which obviate anydetrimental effects upon the image when power has been restored after amomentary power loss.

Briefly, in accordance with a preferred embodiment of the invention, alight valve containing a rotatable disk, a layer of light modulatingfluid coated on the disk, a raster area in which the layer of lightmodulating fluid is bombarded with electrons, and a sump for containinglight modulating fluid are provided, with a portion of the disk beingsubmerged in the sump. Apparatus for maintaining the light modulatingfluid layer smooth and of uniform thickness comprises a stationary plateof predetermined configuration having a flat surface spaced apart fromthe disk at a distance everywhere considerably greater than thethickness of the light modulating fluid layer and at a predeterminedangle with the disk. The plate is situated, with respect to motion ofthe disk, at a location ahead of the raster area. A lower edge of theplate is submerged beneath the surface of the light modulating fluid inthe sump. Additional light modulating fluid, drawn from the sump bycapillary action, partially fills the space between the plate and thedisk above the surface of the light modulating fluid in the sump and, asthe disk rotates at a substantially constant speed, this fluid emergesfrom the space in the form of the light modulating fluid layer at asubstantially constant thickness on the disk.

BRIEF DESCRIPTION OF THE DRAWINGS The features of the invention believedto be novel are set forth with particularity in the appended claims. Theinvention itself, however, both as to organization and method ofoperation, together with further objects and advantages thereof, maybest be understood by reference to the following description taken inconjunction with the accompanying drawings in which:

FIGURE 1 is a partially cutaway side view of a portion of a light valveshowing the fluid thickness regulator means of the instant invention;

FIGURE 2 is a sectional view taken along line 22 in FIGURE 1; and

FIGURE 3 is a sectional view taken along line 33 in FIGURE 2, showingpositions of the rotatable disk and the fluid thickness regulator meansof FIGURES 1 and 2 relative to each other.

DESCRIPTION OF TYPICAL EMBODIMENTS FIGURE 1 illustrates a light valvecontaining the fluid thickness regulator means of the instant invention.The light valve comprises an envelope 10, typically comprised of glass,containing a light output window portion 11 and a sump region 12 holdinga reservoir of light modulating fluid 13. The interior of envelope 10 isevacuated to a low gas pressure.

The light modulating fluid is typically of the polybenzyltoluene typehaving a fluid viscosity of 1,000 centistokes at 60 C., with a vaporpressure in the range of 1O l torr. The fluid contained in sump region12 is that which has drained off of an optically transparent disk 14which is continuously rotated on bearings 15 about a shaft 16, typicallyat a speed of 3 revolutions per hour. A spring 20 is maintained incompression by having its cap 21 affixed to a rigid support member 22which, in turn, is aflixed to envelope of the light valve by anysuitable means (not shown). The opposite end of spring 20 bears againstthe body of a shaft 16. Consequently, a shoulder 23 on shaft 16 urgesbearings to force disk 14 against protuberances 17, which mayadvantageously be formed of fritted glass droplets. These protuberancesare iaflixed to output window 11.

Disk 14 is spaced apart from light output window 11 by a distance ofabout 3 mils so as to permit fluid 18 from sump 12 to rise by capillaryaction and fill the region between the disk and the output window. The 3mil spacing is maintained by protuberances 17, as described in greaterdetail in H. E. Towlson Patent 3,3 85,991, issued May 28, 1968, andassigned to the instant assignee. As pointed out in the aforementionedTowlson patent, adverse effects produced by either a non-uniform fluidcoating on the output surface of the rotatable disk, or by fluidcondensate or droplets on the output window, are thereby eliminated.

A thin film of light modulating fluid 27 is coated on ductive coatingsuch as indium oxide, is carried on rotating disk 14. Coating 24 may bemaintained at any desired potential since a conductive path is formedthrough bearing 15, shaft 16, spring 20, cap 21 and member 22,permitting a continuous electrical connection to coating 24 through astationary connection (not shown) which may be made to member 22. Anaperture 19 in member 22 permits passage of an electron beam 25,originating at an electron gun 26, to be directed toward conductivecoating 24 on disk 14. Disk 14 itself is non-conductive, and ispreferably comprised of glass.

A thin film of light modulating fluid 27 is coated on thin film 24 andthus is situated within the direct path of electrons in electron beam25. Beam 25 is focused and deflected by electron optical means (notshown) within light valve 10 and hence is swept, in raster fashion, overthe surface of light modulating fluid layer 27. The pattern of chargeson layer 27 produced by electron beam 25 causes correspondingdeformations in the thickness of layer 27, resulting in formation ofdiffraction gratings 30. These gratings correspond to the image to beprojected onto a remote display surface. Light from a light source (notshown) positioned behind electron gun 26 impinges upon a lenticular lenssystem 28 formed on the rear wall of envelope 10 and is directed by thelenticular lens system through aperture 19 onto diffraction gratings 30.

By modulation of electron beam 25 through application of suitablepotentials to the electrostatic focus and deflection means, diffractiongratings 30 in fluid layer 27 are selectively controlled. Consequently,the light passing through transparent rotatable disk 14 and outputwindow 11 is selectively controlled and, in conjunction with externallylocated lenses of a Schlieren optical system (not shown), is projectedon a remote display surface (not shown) to form an image representativeof the intelligence modulating the electron beam.

Fresh filtered fluid is supplied from a pump and filter 45, through atube 46 which may discharge near the top of disk 14. This discharge, ofcourse, occurs on the portion of the disk which has passed the rasterarea, in order to avoid interference with diffraction gratings 30. Thisis illustrated in FIGURE 2, described infra. The pump and filter arecontained within a metallic enclosure which is affixed, as by fritting,to envelope 10 of the light valve. The flow of fluid to and from pumpand filter means 45 as indicated by the arrows in FIGURE 1.

A smoothing bar 40 is fitted onto shaft 16 and spaced apart from disk 14by an annular shim 41 which is urged against bearing 15 as a result ofthe force exerted by cap 21 against bar 40. Bar 40 has a substantiallyflat surface 42 which faces disk 14 and is separated from disk 14 by adistance small enough to permit fluid 43 to rise from sump 12 bycapillary action and partially fill the region between the surface 42and disk 14. The upper surface of fluid 43 forms a meniscus boundary 52.

FIGURE 2, which is a sectional view taken along line 22 of FIGURE 1,shows the shape of smoothing bar 40 and the relative positions ofsmoothing bar 40 and tube 46 with respect to disk 14 and raster area 50.Raster area 50 is defined by the area of fluid layer 27 which may bebombarded with electrons from electron beam 25, shown in FIGURE 1.Because the substantially flat surface of smoothing bar 40 is large withrespect to thickness of the bar, the configuration of the bar is that ofa plate. The disk rotates in a counter-clockwise direction as indicatedby the arrow in FIGURE 2. The lower edge of bar 40 dips below thesurface of fluid 13 so that most of the region between bar 40 and disk14 is filled with fluid drawn from sump 12 by capillary action. Bar 40is kept from being rotated by the drag of fluid between the bar and thedisk by supports 44 which extend from rigid support member 22 in adirection substantially perpendicular to the plane of disk 14.Accordingly, plate 40 is held stationary within envelope 10.

Near the periphery of disk 14, bar 40 is urged toward the disk by a pairof compression springs, each of which may be supported within a pair oftwo-piece expandable containers 47 respectively, one piece of each ofwhich is welded to support plate 22. Bar 40 is kept at a predetermineddistance from disk 14 near the periphery thereof by a pair of glassprotuberances or feet 48 fritted onto the surface of the bar facing thedisk. (For simplicity of illustration, containers 47 aand glass feet 48are not shown in FIGURE 1.) As shown in FIGURE 2, bar 40 releases fluidfrom meniscus boundary 52 in a smooth layer 27 of uniform thickness ondisk 14 at a location just ahead of raster area 50, while tube 46discharges fluid onto disk 14 at a location beyond the raster area so asto avoid any interference in the raster area due to uneven thickness offluid on the disk.

In order to achieve a fluid layer of uniform thickness on disk 14, plate40 must be located at a slight angle with respect to disk 14. This isevident in FIGURE 3, which is a top view of a portion of the apparatusillustrated in FIGURES 1 and 2. In FIGURE 3, it is apparent that spacer41 maintains the portion of bar 40 near the center of disk 14 at agreater distance from the disk than the portion of the bar separatedfrom the disk by glass pads 48 near the periphery of the disk. Thereason that bar 40 is spaced at a slight angle with respect to disk 14isv that for any given fluid, operating temperature, and disk speed, thespacing between the barand the disk must vary along the disk radius inorder to compensate for the diflerent tangential velocities of the diskat different points along the disk radius. For any given fluid,operating temperature, and disk speed, spacing Z, representing thedistance between surface 42 and bar 40 and the surface of conductivecoating 24 on disk 14, as measured perpendicular to the plane of thedisk, may be expressed as where K is a constant and R is the location atany point along the radius of disk 14 where spacing Z is to bedetermined, measured from the center of the disk. For a disk having atransparent area of about 4.5 inches in diameter, and using a lightmodulating fluid. of the type previously described, the spacing mayconveniently be 50 mils at the center of the disk and only 24 mils at alocation 2.1 inches from the center of the disk.

Although plate 40 is wedge-shaped and substantially flat, neither thewedge shape nor the flatness is extremely critical. Moreover, onceviscosity and surface tension of the fluid have been established, and adisk speed has been established, fluid thickness can be regulated toachieve the desired depth. The fluid in sump 12, shown in FIG- URE 1,forms meniscus 52 in the space between conductive coating 24 on rotatingdisk 14, and surface 42 of bar 40, as illustrated in FIGURE 1. By properspacing between the bar and the disk, the meniscus radius can be variedalong the disk radius in order to compensate for different tangentialvelocities at diflerent locations along the radius of the disk.Thickness t of the resulting oil film has been found to vary accordingto the following equation:

where C is a constant, r is the meniscus radius at any particular pointalong the disk radius, v is the linear or tangential velocity of thedisk at the point along the disk radius where the meniscus radius hasbeen determined, and 1; is the viscosity of the fluid. Using theaforementioned parameters, a uniform layer of fluid of about 13 micronsthickness may conveniently be formed upon conductive coating 24 onrotating disk 14, although fluid layer thicknesses of from 4 to 24microns have been produced with variations of only about '-.5 micronvariation over the raster area.

Smoothing bar 40 may be made from either glass or metal, and is capableof withstanding a 450 C. bake in air, followed by a 400 C. bake invacuum, both of which are typically employed in fabrication of the lightvalve in which the invention is utilized. By spacing bar 40 at distancesof between 20 and 50 mils from disk 14, high torque requirements are notimposed on the disk and small particles cannot become lodged in thespace between the bar and the disk and scratch the disk. Moreover,because the fluid coated on the disk is drawn by capillary action frombelow the oil surface, foreign material floating in the oil is notpicked up by the disk. The wedge-shaped configuration of the bar and theflatness of the bar are not critical, so that the bar need not befabricated to a high degree of precision and it need not be positionedwith extreme accuracy in the light valve. The smoothing action of thebar is unaffected by momentary power loss, and the bar permitsproduction of an image immediately when the electronic circuitryassociated with the light valve begins operating.

While only certain preferred features of the invention have been shownby way of illustration, many modifications and changes will occur tothose skilled in the art.

It is, therefore, to be understood that the appended claims are intendedto cover all such modifications and changes as fall within the truespirit of the invention.

I claim:

1. In a light valve containing a rotatable disk, a layer of lightmodulating fluid coated on one surface of said disk, a raster area inwhich said layer of light modulating fluid is bombarded with electrons,and a sump containing light modulating fluid, said disk being partiallysubmerged in said sump, apparatus for maintaining the light modulatingfluidlayer smooth and of uniform thickness, said apparatus comprising:

stationary means having a substantially flat surface spaced apart fromsaid one surface of said disk and being situated with respect to motionof said disk at a location ahead of said raster area, said substantiallyflat surface extending above the surface of the light modulating fluidin said sump; and

additional light modulating fluid contained in the space between saidstationary means and said disk, said additional light modulating fluidemerging from said space in the form of said light modulating fluidlayer at a substantially constant thickness on said one surface of saiddisk as said disk rotates at a substantially constant speed.

2. The apparatus of claim 1 wherein said substantially flat surface issituated at a predetermined angle with said disk.

3. The apparatus of claim 1 wherein the separation between saidstationary means and said disk is everywhere greater than the thicknessof said light modulating fluid layer.

4. The apparatus of claim 2 wherein the separation between saidstationary means and said disk is everywhere 1greater than the thicknessof said light modulating fluid ayer.

5. In a light valve containing a rotatable disk, a layer of lightmodulating fluid coated on one surface of said disk, a raster area inwhich said layer of light modulating fluid is bombarded with electrons,and a sump containing light modulating fluid, said disk being partiallsubmerged in said sump, apparatus for maintaining the light modulatingfluid layer smooth and of uniform thickness, said apparatus comprising:

a stationary plate of predetermined configuration having a substantiallyflat surface spaced apart from said one surface of said disk, said platebeing situated with respect to motion of said disk at a location aheadof said raster area and having a lower edge submerged beneath thesurface of the light modulating fluid in said sump; and

additional light modulating fluid drawn from said sump by capillaryaction partially filling the space between said plate and said diskabove the surface of the light modulating fluid in said sump.

6. The apparatus of claim 5 wherein said plate is situated at apredetermined angle with said disk.

7. The apparatus of claim 5 wherein the separation between said disk andsaid plate is everywhere greater than the thickness of said lightmodulating fluid layer.

8. The apparatus of claim 6 wherein said plate is spaced further fromsaid disk near the center of said disk than near the periphery of saiddisk.

9. The apparatus of claim 8 wherein the separation between said plateand said disk is everywhere greater than the thickness of said lightmodulating fluid layer.

10. The apparatus of claim 5 wherein said plate is of generallywedge-shaped configuration.

11. The apparatus of claim 6 wherein said plate is of generallywedge-shaped configuration.

12. The apparatus of claim 8 wherein said plate is of generallywedge-shaped configuration.

(References on following page) 7 8 References Cited JAMES W. LAWRENCEPrimary Examiner UNITED STATES PATENTS v. LAFRANCHI Assistant Examiner2,776,339 1/1957 Arni 178-7.5 1 3,164,671 1/1965 Schilling 17s 7.s

3,385,991 5/1968 ToWlsOn 313-91 5 1787.5, 7.82; 313232; 350161, 162

